The invention process is concerned with the enhanced recovery of oil from underground formations. More particularly, the invention relates to a thermal method for recovering hydrocarbons with parallel horizontal wells.
Horizontal wells have been investigated and tested for oil recovery for quite some time. Although horizontal wells may in the future be proven economically successful to recover petroleum from many types of formations, at present, the use of horizontal wells is usually limited to formations containing highly viscous crude. It seems likely that horizontal wells will soon become a chief method of producing tar sand formations and other highly viscous oils which cannot be efficiently produced by conventional methods because of their high viscosity. Most heavy oil and tar sand formations cannot be economically produced by surface mining techniques because of their formation depth.
Various proposals have been set forth for petroleum recovery with horizontal well schemes. Most have involved steam injection or in situ combustion with horizontal wells serving as both injection wells and producing wells. Steam and combustion processes have been employed to heat viscous formations to lower the viscosity of the petroleum as well as to provide the driving force to push the hydrocarbons toward a well.
A system of using parallel horizontal wells drilled laterally from subsurface tunnels into the lower portion of a tar sand formation is disclosed in U.S. Pat. No. 4,463,988. The described process injects a displacing means such as steam into the boreholes to cause hydrocarbons to flow into the lower portion of the lateral boreholes and be produced to the surface.
U.S. Pat. Nos. 4,491,180 and 4,515,215 describe the conversion of steam injection into water injection in viscous oil recovery processes. U.S. Pat. No. 4,260,018 discloses a method for steam flooding a dipping formation from the updip end to the downdip end. This process injects hot water through separate injection wells located between the steam bank and the outcrop end of the reservoir to act as a buffer zone to prevent steam from escaping the formation.
FIGS. 1, and 2 illustrate the practice of the invention on substantially parallel horizontal wells. FIG. 1 is a top view and FIG. 2 is a side view along line 2--2 of FIG. 1.